A newly designed hygroscopic condenser humidifier was evaluated to assess efficacy of providing moisture to the airways in patients whose upper airways had been bypassed. With its use, the relative humidity of inspired gas fell with both increasing tidal volumes and especially increasing F10(2) due to the intrinsic dryness of medical oxygen. Under conditions other than high volumes and inspired oxygen, humidification appeared adequate. The device obviated many complications encountered with conventional heated nebulizers. It does add some degree of resistance in the ventilatory circuit which might be stressful during spontaneous breathing.